The incident reportedly took place when Costa reacted angrily to what was apparantly a robust challenge by the Brazilian midfielder. According to the British media, Oscar produced a knee-high lunge to Costa’s legs after the Spain international had initially gone in hard on him.

There was reportedly a heated exchange of words between the two players and the duo had to be separated by those present at the scene.

However, Chelsea officials insist that the situation was soon brough under control and Oscar and Costa were joking about the incident at the end of the training session.

Although Costa has developed a reputation for losing his temper after a series of on-field confrontations, fellow Chelsea players have mostly blamed Oscar for the incident.

“Oscar’s challenge was outrageous, it was straight into the knee of Costa and could have done him some real damage. That sparked a brawl between them and the other players had to stop it,” a player was quoted as saying by the Telegraph on Friday.

Oscar later took to social media network Twitter to downplay the incident.

“For those who are talking to me and @diegocosta struggle today in training he’s lying, he’s one of my best friends and never fight,” the Brazil international wrote.

Despite the incident, both Costa and Oscar are expected to be involved in the match against Scunthorpe this weekend.